Electrothermal device for cyclic contact operation



March 8, 1966 E. w. MGMULLEN 3,239,632

ELECTROTHERMAL DEVICE FOR CYCLIC CONTACT OPERATION Filed Oct. 4, 1962 :t E 25 59 n D 2 I NVENTOR.

EDWARD w. MCMULLEN L BY QJ, 1 juf, 'L' f I f ATTORN EY United States Patent 3,239,632 ELECTROTHERMAL DEVICE FOR CYCLIC CGNTACT GPERATIN Edward W. McMullen, Nutley, NJ., assigner to G-V Controls Inc., Livingston, NJ., a corporation of New Jersey Filed Get. 4, 1962, Ser. No. 228,414 12 Claims. (Cl. 2410-122) This invention relates to an electrothermal device for cyclic contact operation-ie., for the cyclic opening and closing of a pair of contacts. Such a device when used for the repetitive switching on and off of an electric lamp is frequently termed a thermal flashen but no limitation to use for that purpose is intended.

Such devices a-s conventionally constructed sucer from several disadvantages. These, hereinafter more detailedly described, include a propensity to inter-contact arcing; a sensitivity of the length of their cycle of operation, and of the intervals of contact openness and closure within the cycle, to small random influences; diiculty in establishing desired lower frequencies of operation; necessity to operate the device near its saturation point, at relatively high average temperature and with excessive power consumption; marked sensitivity of the frequency and intra-cyclic intervals to changes in the supply voltage; inability to adjust the relative intervals of contact openness and closure While maintaining unchanged the frequency of operation; and the need to endure one or more initial cycles, when any operation of the device is initiated, of excessive duration and abnormal interval relationship.

Objects of the invention are to obviate the individual ones of the abovementioned disadvantages; other objects are to obviate groups of them, and a particular object is to obviate them all. An object is the provision of a generally improved device of the type indicated by the title. Allied and other objects will appear from the following description andthe appended claims.

Devices of the type herein dealt with inherently comprise some form of actuating mean-s, whose function is at least to operate the contacts which are to be repetitively opened and closed-ie., the output contacts-and which is positionally responsive to the-temperature of a heatable element within the device. According to the invention electric current is supplied to the heater which heats that element through a switch which is opened and closed by the actuating means at respectively different positions of that means; the output contacts are also opened and closed by that actuating means, but while it is away from at least one of the positions just mentioned in connection with the switch. More specifically, those contacts may be operated by the actuating means while it is away from both of those positions, or by that means at a single position thereof which in turn may be intermediate between those positions. Further according to the invention 4the difference of positions of the actuating means at which it will open and close the heater-circuit switch may be established by an arrangement which is of toggle or other snap-action variety, or which is associated with that switch, or which is both of that variety and associated with that switch. Further according to the invention separate means are provided for the adjustment of the switch opening and closing and for the adjustment of the outputcontact opening and closing.

In the detailed description of the invention hereinafter set forth reference is had to the accompanying drawing, in which:

FIGURE l is a view, cross-sectional in the vicinity of the base and otherwise elevational with cover removed, of an electrothermal device embodying the invention, to-

gether with a schematic showing of an associated source of current;

FIGURE 2 is a cross-sectional View along the line 2-2 of FIGURE 1; f

FIGURE 3 is a cross-sectional View along the line 3 3 of FIGURE l;

FIGURE 4 is a schematic illustration of the device of FIGURE 1;

FIGURE 5 is a curve showing a typical action of the device of FIGURE 1, together with certain other curve-s for comparative purposes;

FIGURE 6 is a fractional view similar to a portion of FIGURE 1 but illustrating an alternative arrangement of the contacts;

FIGURE 7 is a view generally similar to FIGURE 1 but illustrating the electrothermal device with a modified form of heatable element and heater; and

FIGURE 8 is a view generally similar to FIGURE 1 but illustrating the electrothermal device with a further modified form of heater.

The electrothermal device of FIGURE 1 is shown by way of example as assembled to a base 10 of the octal variety widely used for radio tubes and the like and comprising a generally disc-shaped member 11 and a tubular keyed pilot cylinder 9 molded, integrally with each other of insulating material, with eight metallic pins each passing throughthe member 11 and extending outwardly (as shown in FIGURE 1, leftwardly) therefrom, those pins being equidistantly arranged in a circle about the pilot cylinder 9 (as seen in FIGURE 2) and being sequentially numbered 1 through 8. Inwardly (as shown in FIGURE 1, rightwardly) from the pins 2 and 3 there may extend respective rigid wire lugs 12 and 13, the lug 13 being desirably offset away from 12 as indicated at 13. Along the inner .surface of the member 11, between the pins 4 and 7 and held under suitable shouldering on those pins, there may extend a metallic strap 14 hereinafter referred to. ,Along that inner surface and held under similar shouldering on pins 1 and 8 may be a small approximately oval metallic plate 16, and held under similar shouldering on pins 5 and 6 may be a corresponding plate 18; from the respective edges of those plates which face each other bottom of the figures) are parallel.

there may be folded inwardly away from the member 11 at right angles thereto respective mounting ears or lugs 17 and 19 of generally triangular elevation and of which at least the furtherfextending portions (seen toward the In the illustrated device the main frame 20, which may be of relatively wide U-cross-section channel metal (the U being inverted as viewed in FIGURES 1 and 3), may just tit between the lugs 17 and 19 and may be supported by spot-welding those lugs to the end portions of its sides disposed toward the base 10.

Effectively hinged to the top (as viewed in FIGURE 1) of the frame 20 at a point, designated as D, somewhat spaced toward the base 10 from the free end of the frame is an arm 30 which may be of somewhat wider U-cross-section channel metal (also inverted as viewed in FIGURES l and 3) and which from the point D may extend toward the base 10- at an vacute angle to the frame. The hinging may be accomplished by extending the crosssectionally central portion of the arm 30, at the end of the arm remote from the base 10, to form a projection 29 and spot-welding that projection to the top of the frame; the material of the arm will be thin enough so that an effective hinge will be created along the imaginary line between the arm proper and that projection (i.e., at the point D), In its free end portion (i.e., that toward the base lll) there is secured to the arm 30 a small platform 32 upwardly displaced from the arm; this platform may be constituted by the central section of an inverted U-shaped metallic bracket 31 whose sides just straddle and are spot-welded to the sides of that portion of the arm 3i).

In its end portion remote from the base 1t) there is secured to the frame 2t) a small platform 22 upwardly displaced from the frame; this platform may be constituted by the central section of an inverted U-shaped metallic bracket 21 whose sides just straddle and are spot-welded to the sides of that portion of the frame.

In FIGURES l and 3 a heatable element 40 is shown in the form of a strip 40 of metal of which the end portion toward the base is spot-welded to the top of the platform 32 and the other end portion is spot-welded to the top of the platform 22. The strip 40 will be thin enough so that an effective hinge will be created at each of its end portions where that passes over the edge of the respective platform (i.e., at points E and C). The expansion of the strip or element 40 with heat is intended to result in an increasing of the separation between points E and C, yet the strip may be insufficiently rigid itself to insure that such expansion will not buckle the strip instead of increasing that separation. Positively to insure that separation increase instead of that buckling there may be applied to the arm 30 near its end disposed toward the base 10 a downward force whose influence on that arm will be a bias to counterclockwise rotation (as viewed in FIGURE 1) about the point D and which will therefore bias the platform 32 to a downward movement which will progressively (but in stepped-down magnitude) increase its separation from platform 22. Conveniently to apply this force, an upright U-shaped bracket Z8, with its sides just straddling and spot-welded to the sides of arm 30, may hang down from that arm in surrounding relationship to the frame 20, and from the bottom of this bracket upwardly to the bottom of the cross-sectionally central portion of the frame (see FIGURE 3) there may exten-d a helical spring Z7 compressed between the bracket and the frame.

It may here be observed that if the frame 20, bracket 21, arm 30, bracket 31 and strip 40 all be of similar metal (of which a desirable choice is stainless steel), then although all those elements be uniformly heated or cooled (as by varying ambient temperatures) nevertheless the angular shape of the structure formed by those elements or in ultimate terms the shape of the triangle C-D-E, and thus the angle between the arm and the frame 20, will remain constant. The structure is thus compensated for ambient-temperature variations; in terms sometimes used the strip 4t) is an element expansible by heat locally supplied to it while the arm 30, being the principal other one of the ve elements just discussed, is a compensating element.

An electric heater 45 is arranged to heat the element 40. To provide for that heater very thin mica cards 46 may be placed one immediately above and one immediately below the strip; the heater itself may be a suitable resistance wire or ribbon wound about the sandwich constituted by the cards and the intervening strip, suitable electrical terminations 47 (insulated, as by the mica cards 46, from the strip being provided for the extremities of the 4heater. The supply of current to the heater of course results in a substantial heating of the heater and of the element 40 whose resulting expansion, now unaccompanied by expansions of 20, 21, 30 or 31 other than minor ones which may result from incidental transfers of heat to them from the heater and strip 4t), in turn results in a stepped-up decrease of the separation of point E from the frame 2i-i.e., a rocking of the arm 30 counterclockwise about point D--and thus a change of the angular shape of the triangle C-D-E.

For the sake of clear illustration in FIGURE 1 the mica cards 46 are shown slightly spaced above and below the strip 40, but it will be understood that actually they will be in Contact with it, as seen in the case of the upper card in FIGURE 3 in which for clarity the heater 45 is not shown.

The arm 30, which has just been seen to a positionally responsive to the temperature of the element 40 (i.e., angularly responsive to the temperature of that element relative to associated elements), may conveniently be considered as an actuating means by which elements not yet described are operated. One of those elements may be a pair of contacts 60 and 61 of which the operation is their opening and closing from and against each other by the arm 3i). rihe contact 61 may for example be a positionally fixed one, carried on a short lug 62 which ex tends at right angles to the base member 11 and which forms one leg of a right `angle bracket whose other leg is spot-welded to the inner surface of the strap 14 abovementioned so as to position the contact 61 slightly above and facing .toward the axis of the base 10. To carry the contact 6i? there may be provided a relatively light metallic leaf spring arm 59 whose end portion remote from the base 10 may be spot-welded to the top of the frame 20 near the longitudinal mid-point of that frame and which from that end portion extends toward the base, at an acute angle to the frame, to bring its other end portion directly below the contact 61, where the contact 60 is secured on top 0f it and by it is biased upwardly into closure against the Contact 61. The arm 30 may be rendered an actuator for the pair of contacts 611-61 through the medium of a screw 35 projecting toward (and at times into abutment against) the top of the spring arm 59 through a rigid lug 34 which is secured on top of and projects toward the base 10 from the free end portion of the arm 30.

The basic structure described above will be recognized as constituting a thermal relay. It is generally similar to that shown and described in U.S. Patent No. 2,948,788 to William C. Broekhuysen in and with relation to FIG- URES 4, 5 and 6 of that patent, to which reference may be had as to details unnecessary herein to show or describe.

The present invention is particularly concerned with the use of a device which constitutes a thermal relay, preferredly one of the general form above described, for the repetitive opening and closing of a pair of contacts, for example the contacts 60-61 of the present FIGURES 143. For such use it is known to supply current from an appropriate source to the heater (e.g., 45) serially through a switch which will be opened in response to the heating and closing in response to the cooling of thel heatable element (e.g., 40), for which switch it is known to use the switch constituted by the same contacts (e.g., 61E-61) as are to be repetitively operated `by the device. It wiil be understood that were this to be done in the case of the FIGURE l-3 structure, then when current was first supplied the heating of the heater 45 and element 4t) would cause the counterclockwise rotation of the arm 30, which in turn would rst bring the end of screw 35 down into abutment against `spring arm 59 and would then progressively apply an increasing downward force on that spring arm; as that force passed through the Value just sufficient to counterbalance the upward bias of that spring arm, the contact 60 would begin to move away from the contact 61 thus opening the contacts.

The contact opening would interrupt the supply of current to the heater whereupon its temperature would begin at once, and that of the element 41B almost 'at once, to drop; a lsmall drop of the element temperature would. quickly result in sufficient clockwise rotation of the arm 39 to close the contacts. That contact closure would reestablish the supply of current `to the heater whereupony its temperature would begin at once, and that of the element 40 almost at o-nce, to rise again; a small rise of the element temperature would quickly reopen the contacts, interrupting again the supply of current to the heater whereupon its temperature would begin at once, and that of the element 40 almost at once, t@ drop again and thus to cause again the closure of the contacts-and so on in a sustained mechanical oscillation of the arm 30 and a repetitive or cyclic opening and closing of the contacts 6ft-61 thereby. indicated by the curve I of FIGURE 5, wherein the abscissae represent time and the ordinates represent downward displacement of the arm 30 (as seen at screw 35) from its ambient-temperature position (i.e., its position when the entire device is at ambient temperature), and wherein the ordinate S represents the limiting or saturation displacement which would be reached by the arm only on long-sustained and uninterrupted supply of current from the source to the heater. The `frequency of the cyclic armdisplacement would be sharply higher,

and the amplitudefof that cyclic displacement sharply' lower, the tighter be the thermal coupling between the heater 45 and the heatable member 40; for the sake of simple illustration curve I shows av frequency which is substantially lower, and an amplitude which is substantially higher, than would in practice be likely, and therefore is' appropriate to very loose thermal coupling between heater and member.

There are several disadvantages' in such an arrangement and operation' as have just been outlined. One is that because the amplitude of the arm oscillation is relatively small (typically much smaller than illustrated in FIG- URE 5) the speed with which the contacts open and close will `be very little, leadingin many cases to serious inter-contact arcing. -Asecond disadvantage, also resulting from the relatively small amplitude of arm oscillation, is that small random influences may result in considerably varying amplitudes fromV one cycle to the next and thus in considerably varying durations of the cycles and of the contact-open and contact-closed intervals, -some such irregularity being indicated in curve I. A third disadvantage is'that it is difficult, even with heatable. ele-' This action is approximately render the first further 4than the second from the arms ambient-temperature position); the operation would then be as approximately indicated in curve II in FIGURE 5, on which curve the points O may be taken as those of v contact opening and the points K as those of contact through the contacts 60-61 but instead through ya distinct switch which is also opened and closed by the arm 30, by arranging the device s'o that there will be a substantial differencev between the positions of the arm 3i) at which that switch will be opened and closed, and by arranging the device so that the contacts ultimately to be cyclicly operated (e.g., 60-61) will be opened and closed by the arm while it is away from at least one if not both of the positions last mentioned-typically, will be opened and closed by the arm intermediately in its travels between those positions, and for example at substantially ments far more massive than that illustrated in FIGURE 1, to achieve the lower frequencies of contact operation which are frequently desireda disadvantage which can only limitedly be coped with by relatively loose thermal coupling between heater and heatable element, which itself entails a chain of other disadvantages starting with excessive consumption of power `from the source.

A fourth disadvantage is that if the intra-cyclic intervals during which the contacts are open areto be somewhere near the same as those during which they are closed-as is more usually desired than not-it is necessary so to adjust the system that the displacement range through which the arm 30 -oscillates lies relatively near the saturation displacement S,or well above a displace- Y ment of S/ 2; this not only `exaggerates the smallness of oscillation amplitude and the abovementioned disadvantages which ow from that, but also entails operation at relatively higher average temperatures with resulting 1ncrease of power consumption. kA fifth disadvantage, present when the device is thus operated near the saturation displacement S, is that the frequency of operation and the intra-cyclic intervals are markedly influenced by variations of the voltage of the source of heater current. A sixth disadvantage is that the relation between the intracyclic intervals of contact openness and contact closure cannot be altered without markedly affecting the frequency of the contact operation. A seventh disadvantage, especially with anything like equal intra-cyclic intervals, is that when the device is irst placed in operation there will be an initial cycle (and in some constructions, a group of initial cycles) of excessive duration and abnormal interval relationship before the cyclic operation approaches stability.

The first and `second and, if relatively short intra-cyclic intervals of contact closure can be tolerated, the thrid of these disadvantages may be obviated by the incorporation in the device of some means which will displace one from the other the positions of the arm 30 at which the contacts 60-61 open and that at which they close (i.e., will a single position of the arm as is the case with the contacts -61 already described. Means to render substantially different theswitch-opening and switch-closing positions of the arm`30 may -take any of a variety of forms and may be incorporated in the device in any of various'positions; in the illustrated embodiments of the invention -those -means are of toggle arrangement and arev incorporated in the abovementioned switch through which the heater current is supplied.

The references of the preceding paragraph to positions of the arm 30 may alternatively be read as references toy the temperature elevation' (i.e. elevationA above ambient temperature) lof the element 40,' in view of the relationships set forthat the beginning of the eighth preceding paragraph. Correspondingly they ordinate of the curves lof FIGURE 5 may be taken as'temperature elevations of the element'40'-S being then the saturation temperature elevation of that element.

two positions, throwable to the second ofits positions back from the second to the first position will occur.

Schematically this switch appears in its irst position in FIGURE4 4, wherein the compressed spring 74 typifies the biasing means and wherein the compressed spring 73 4intervening between the free ends of the pivoted pole 72 and the pivoted arm 72 typifies the snap-action or toggle arrangement. As appears in the schematic FIGURE 4, the switch 70, although it may have two contacts between which the pole'72 may be thrown, needs in the practice of the invention to use only that one of those two contacts which renders it a normally closed single-throw switch. y(The remainder of the schematic FIGURE 4 will be recognized as a simplified schematic showing of the structure already described with relation to FIGURES 1-3; it requires no special comment, other than to note that the downward v biasing force on the arm 30 has for simplicity been To provide for the physical incorporation of the switch 70 in the device of FIGURES 1-3 there may be provided an upright J-cross-section bracket 75 whose shorter vertical part may for example be spot-Welded against the inner surface of one of the sides of the frame 2t?, for example yabout opposite the longitudinal midpoint `of the arm 30, and whose longer vertical part may then stand laterally displaced from the frame. The switch 7) may then be fastened to that longer vertical part -as by screws 76, with the switch button 71 projecting upwardly. Between the -heads of those screws and the switch there may be clam-pcd a vertical plate 77 which extends, somewhat more remote from the base 10 than is the button 71, a little above the top of the switch and from the upper portion of which a stud 78 may extend laterally over tihe switch. Pivotally assembled on this stud may be the end portion of a light lever 79 which therefrom extends toward the base 10 and rests on top of the button 71.

To provide for the opening and closing of the switch 70 by the actuating means or arm 30, the lower portion of the vertical leg of an inverted L-cross-section bracket 37 may be spot-welded to the side of the arm 30 close to the end of the latter toward base 10; from the top of `that leg the other leg of the bracket 37 extends both laterally and away from base 10 so as to bring its free end portion over the free end portion of the lever 79. Through that bracket free end portion there is threaded a `screw 38 whose lower extremity may be brought as near to contact with the top of the lever 79 as may be desired. It will be obvious that as the arm 30 is rocked counterclockwise in response to heating of the element 40 the screw 33 will be brought fully into contact with the lever 79 and will rock that lever downwardly to displace the button 71 inwardly and thus to open the switch 70, which will be re-closed only when the arm 30 has subsequently rocked clockwise to a somewhat higher position that at which the switch opened.

The difference between the positions of the button 71 at which the switch 70 will be `opened and closed, together with the various lever ratios involved, may be so established that the difference between the arm 30 displacement (from its ambient-temperature position) at which that switch will be opened and that smaller arm displacement at which it will be re-closed is -a substantial part-for example, about half--of the saturation displacement of the arm. The screw 38 is desirably so adjusted that the switch 70 will be opened when the arm 30 is displaced by a major fraction-for example, about 65%-of it saturation displacement. In the same example, then, the switch 70 will be re-closed when the arm 30 has returned to a displacement of about 15% of `its saturation displacement. This is approximately indicated b-y the curve III of FIGURE 5, wherein the points P may be considered those of opening, and the points L those of re-closing, of the switch 70. It of course follows from what has been said above that the ordinate of the points P alternatively represents about 65% of the saturation temperature elevation of the element 40, and that the ordinate of the points L correspondingly represents about of that saturation elevation.

Obviously the intra-cyclic interval during which the switch 70 will be closed is much shorter than that during which it will be open-but this in no way affects the relative apportionment of the intervals of openness and closure of the contacts 60-61 of ultimate interest. By adjustment of the screw 35 those contact 60-61 intervals may be relatively apportioned as desired. Thus with a relatively low adjustment of the screw 35 (so that when the arm is at ambient-temperature position the screw end is close to the spring arm 59) the contacts 611-61 may be made to open and close as the arm 30 drops and rises through the position indicated by the line X in FIGURE 5, resulting in each cycle in long intervals of contact openness and short intervals of contact closure; reversely, by a relatively high adjustment of the screw the contacts may be made to open and close as the arm 3() drops and rises through the position indicated by the line Z, resulting in each cycle in short intervals of contact openness and long intervals of contact closure; intermediately, by a medium adjustment of the screw 35 the contacts may be made to open and close as the arm 30 drops and rises through the position indicated by the line Y, resulting in each cycle in equal intervals of contact openness and closure. Obviously the references of this paragraph to position of the arm 30 may alternatively be read as references to the temperature elevation of the element 40.

Arcing at the switch (70) which opens and closes the heater circuit is minimized both by reason of more abrupt arm-30 movement (particularly at the time of opening of the switch) as well as by reason of the snap-action nature of the switch. The large amplitude of oscillation of the arm substantially obliterates the effects, on cycle and interval lengths, of small random inuences. Low frequencies of operation of the contacts 60-61, appropriate to the inherent characteristics of the heatable element 40, are ac-hieved without limitation to short intervals of contact closure. The displacement range throughout which the arm 30 oscillates may readily be kept nearer to the arms ambient-temperature position than to its saturation displacement; this, aided by the relative shortness of the interval of switch 70 closure compared to that of openness, results in relatively low-average-temperature low-consumption operation. The relatively long interval of switch 70 openness, during which the behavior of the heater and element 40 is of course a cooling whose rate is independent of the source voltage, insures small effect of source-voltage variation on frequency and intracyclic intervals. On the other hand the intervals of contact 69-61 openness and closure may be adjusted at will without sensibly affecting the frequency of operation. The initial cycle will be of shorter-than-normal rather than very excessive duration, consisting of a shorter-thannormal interval during which the contacts will be in their initial (e.g., closed) condition followed by a quite normal interval of the opposite condition. Thus (and without any reliance on loose thermal coupling between heater and heatable element) all the disadvantages mentioned above are at once eliminated.

Description of the FIGURE l-3 structure may be completed by noting that the pins 2 and 3 are used for the heater circuit and therefore are shown connected to an appropriate external current source 100; internally of the device the wire lug 13 leading from the pin 3 may be connected directly to one end of the heater, while the wire lug 12 leading from the pin 2 may be connected through switch 70 to the other end of the heater, no part of the heating circuit being connected to the frame 20. On the other hand the contact is conductively connected through the spring arm 59 to the frame 20 and may be electrically connected to by connection either to pin 8 or alternatively to any one of the pins 1, 5 and 6, while contact 61 is conductively connected through the bracket 63 to strap 14 and may be electrically connected to by connection either to pin 7 or alternatively to pin 4. A deep cup-shaped cover (suitably apertured to provide access to the screws 35 and 39) may be fitted around the internal components of the device and secured to suitable shouldering around the peripheral part of the base element 11.

While the serially arranged switch must remain a normally closed element opened by displacement of the arm 3i) from ambient-temperature position, the contacts 60-61 may constitute either a normally closed opened by such a displacement (as in FIGURES 1-3) or a normally open element closed by such displacement. Their modification to the latter arrangement has been shown in the fractional FIGURE 6, wherein the contact 60 is replaced by a contact 60 on the bottom of spring arm 59 and contact 61 is replaced by a contact 61', underneath 60', carried on top of the extending portion of a nowupright L-shaped bracket 63 substituted for the bracket 63. The relative intervals of contact openness and closure may again be adjusted by screw 35-it being understood that now downward displacements of the arm 34 greater than those required just to close the contacts will be accompanied by a bowing of spring arm 59. j

The heatable element 40 and heater 45 of FIGURES 1-3 are of a form useful for intermediate frequencies of operation of the switch 70 and contacts 60-61, for example of the very general order of 5 to 15 cycles per minute. For higher frequencies, for example up to 60 or more per minute, it is desirable to repalce 40 and 45 by an arrangement in which -t-he heatable element consists of one or more heatable wires which themselves form their own heater, as illustrated in elevation in FIGURE 7. Herein the heatable wires 145 extend, for example electrically in series but mechanically in multiple, between stacks 146 of mica cards which are held together by suitable straps 148, of which the one toward the base is fastened to a flexible lug 33 extending from t-he platform 32 and the one remote from the base is fastened to a flexible lug 123 which in turn is fastened to a projection 122 formed from the platform 22; the two electrical terminals of the group of wires 145 are designated as 147. The constrution thus briey described may be similar to that shown and described in the abovementioned U.S. patent to Broekhuysen in and with relation to FIGURES 7 through 10 thereof and need not herein be further detailed. Mention may be made of the fact that in FIGURE 7 of the drawings herein the vertical dimensions and spacings of elements have been somewhat exaggerated and the lever 79 has been shown as replaced by a stepped or oifset lever 79'; this has been done solely for the sake of more lucid illustration, and it will be understood that in practice those dimensions and spacings may be smaller and that lever again a straight one.

For lower frequencies, for example down to 1 cycle or less per minute, it is desirable to replace 40 and 45 of FIGURES 1-3 by a heatable element 240 and a heater (not shown) contained within that element, as illustrated in the elevational FIGURE 8. Therein the element 240 is shown secured to the flexible lug 33 extending from the platform 32 and to a flexible lug 23 extending from the platform 22; the terminals of the internal heater are designated as 247. The construction of the heatable element 240 and of the heater contained therein may be similar to that shown and described in the abovementioned U.S. patent to Broekhuysen in and with relation to FIGURES l, 2 and 16 thereof and need not yherein be further detailed.

While I have disclosed my invention in terms of particular embodiments thereof, it will be understood that I intend thereby no unnecessary limitations. Modifications in many respects will be suggested by my disclosure to those skilled in the art, and such modifications will not necessarily constitute departures from the spirit of the invention or from its scope, which I undertake to dene in the following claims.

I claim:

1. An electrothermal device comprising in combination a heatable element, an electric heater thermally coupled to said element for elevating its temperature above ambient temperature, actuating means mechanically coupled to said element and positionally responsive to its temperature elevation, a heating circuit, in which said heater is serially connected, further including a switch opened and closed by the actuating means whereby intermittently to elevate the temperature of said element and in turn to cause a cyclic switch-opening-and-closing movement of the actuating means, means for establishing at substantially different values each essentially independent of ambient temperature the respective temperature elevations of said element at which said switch is opened and closed, and a pair of output contacts, external to said heating circuit and of which one is mechanically coupled to the actuating means, cyclicly opened and closed by the actuating means While the temperature elevation of said element differs substantially from at least one of said abovementioned respective elevations.

2. The subject matter claimed in claim 1 wherein said pair of output contacts is cyclicly opened and closed by said actuating means while the temperature of said element differs substantially from both of said respective elevations.

3. The subject matter claimed in claim 1 wherein said pair of output contacts is cyclicly opened and closed by said actuating means while the temperature of said element is intermediate between said respective elevations.

4. The subject matter claimed in claim 1 wherein said pair of output contacts is cyclicly opened and closed by said actuating means at substantially a single temperature elevation of said element.

5. The subject matter claimed in claim 4 wherein said single temperature elevation is intermediate between said respective elevations.

6. The subject matter claimed in claim 1 further including means for adjusting the values of said respective temperature elevations, and means separate from said lastmentioned adjusting means for adjusting the intracyclic intervals of openness and closure of said output contacts.

7. The subject matter claimed in claim 4 further including means for adjusting the value of said single temperature elevation.

8. The subject matter claimed in claim 1 wherein said means for establishing at substantially diierent values said respective temperature elevations is comprised in said switch.

9. The subject matter claimed in claim 1 wherein said means for establishing at substantially diiferent values said respective temperature elevations is a snap-action means.

10. The subject matter claimed in claim 1 wherein said means for establishing at substantially different values said respective temperature elevations is a snap-action means.

11. The subject matter claimed in claim 1 wherein said pair of output contacts is cyclicly opened and closed by said actuating means while the temperature elevation of said element is less than half of its saturation elevation.

12. The subject matter claimed in claim 1 further including means for adjusting the intra-cyclic intervals of openness vand closure of said output contracts while maintaining substantially unaltered the frequency of their opening and closing.

References Cited by the Examiner UNITED STATES PATENTS 1,215,665 2/1917 Landis 200-122 2,496,135 1/ 1950 Sedwitz 200-122 2,817,731 12/ 1957 De Falco 200-122 2,939,933 6/ 1960 Manganaro et al. 200-122 2,948,788 8/ 1960 Broekhuysen 200-122 2,969,917 1/1961 Nason 200--122 3,017,477 1/ 1962 De Leonardis 200--122 3,062,937 11/ 1962 Flanagan 200-122 FOREIGN PATENTS 19,906 3/ 1909 Great Britain. 536,701 5 1941 Great Britain.

BERNARD A. GILHEANY, Primary Examiner. 

1. AN ELECTROTHERMAL DEVICE COMPRISING IN COMBINATION A HEATABLE ELEMENT, AN ELECTRIC HEATER THERMALLY COUPLED TO SAID ELEMENT FOR ELEVATING ITS TEMPERATURE ABOVE AMBIENT TEMPERATURE, ACTUATING MEANS MECHANICALLY COUPLED TO SAID ELEMENT AND POSITIONALLY RESPONSIVE TO ITS TEMPERATURE ELEVATION, A HEATING CIRCUIT, IN WHICH SAID HEATER IS SERIALLY CONNECTED, FURTHER INCLUDING A SWITCH OPENED AND CLOSED BY THE ACTUATING MEANS WHEREBY INTERMITTENTLY TO ELEVATE THE TEMPERATURE OF SAID ELEMENT AND IN TURN TO CAUSE A CYCLIC SWITCH-OPENING-AND-CLOSING MOVEMENT OF THE ACTUATING MEANS, MEANS FOR ESTABLISHING AT SUBSTANTIALLY DIFFERENT VALUES EACH ESSENTIALLY INDEPENDENT OF AMBIENT TEMPERATURE THE RESPECTIVE TEMPERATURE ELEVATIONS OF SAID ELEMENT AT WHICH SAID SWITCH IS OPENED AND CLOSED, AND A PAIR OF OUTPUT CONTACTS, EXTERNAL TO SAID HEATING CIRCUIT AND OF WHICH ONE IS MECHANICALLY COUPLED TO THE ACTUATING MEANS, CYCLICLY OPENED AND CLOSED BY THE ACTUATING MEANS WHILE THE TEMPERATURE ELEVATION OF SAID ELEMENT DIFFERS SUBSTANTIALLY FROM AT LEAST ONE OF SAID ABOVEMENTIONED RESPECTIVE ELEVATIONS. 